Various fuel delivery systems may be used to provide a desired amount of fuel to an engine for combustion. One type of fuel delivery system includes a port fuel injector for each cylinder of the engine to deliver fuel to respective cylinders. Still another type of fuel delivery system includes a direct fuel injector for each cylinder of the engine to deliver fuel directly to respective cylinders.
Engines have been described that utilize multiple fuel injector locations for each cylinder to deliver different types of fuel. One example is described in the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. Specifically, the Heywood et al. papers describe directly injecting ethanol into the cylinders to improve charge cooling effects, while relying on port injected gasoline for providing the majority of the combusted fuel over a drive cycle.
However, the inventors herein have recognized several issues with these systems. As one example, one of the gasoline or ethanol fuels may be used up by the engine before the other fuel, thereby potentially affecting performance characteristics of the engine. For example, if the ethanol is exhausted before the gasoline or available in reduced quantity, the occurrence or intensity of engine knock may consequently increase, or the direct fuel injector may over heat as a result of its discontinued delivery of the ethanol fuel to the engine.
To facilitate the delivery of two or more different fuels, a fuel delivery system for an internal combustion engine has been provided herein by the inventors. As one example, the fuel delivery system may comprise a first fuel injector configured to deliver fuel to a cylinder of the engine; a second fuel injector configured to deliver fuel to the cylinder of the engine; a fuel storage tank; a fuel delivery circuit including a first fuel passage fluidly coupling the fuel storage tank to the first fuel injector and a second fuel passage fluidly coupling the first fuel passage to the second fuel injector; a fuel pump configured to supply fuel from the fuel storage tank to the fuel delivery circuit; a pressure relief valve arranged along the second fuel passage and a control system. The pressure relief valve configured to: close the second fuel passage when fuel is supplied from the fuel storage tank to the fuel delivery circuit at a first pressure; and open the second fuel passage when fuel is supplied from the fuel storage tank to the fuel delivery circuit at a second pressure. The fuel delivery system may further include: a second fuel storage tank; a third fuel passage fluidly coupling the second fuel storage tank to at least one of the second fuel injector and the second fuel passage; and a second fuel pump configured to supply fuel from the fuel storage tank to the third fuel passage.
As one example, the control system may be configured to: during a first operating condition, operate the fuel pump to supply fuel from the fuel storage tank to the fuel delivery circuit at the first pressure while operating the first fuel injector to deliver to the cylinder the fuel received from the fuel storage tank. The control system can be further configured to operate the second fuel pump to supply fuel from the second fuel storage tank to the second fuel injector via at least the third fuel passage while operating the second fuel injector to deliver to the cylinder the fuel received from the second fuel storage tank. During a second operating condition, the control system can be configured to operate the fuel pump to supply fuel from the fuel storage tank to the fuel delivery circuit at the second pressure while operating the first and the second fuel injectors to deliver to the cylinder the fuel received from the fuel storage tank.
In this way, a fuel may be selectively supplied from a fuel storage tank to two or more different fuel injectors of a common cylinder of the engine according to operating conditions. For example, where fuel in a second fuel storage tank is exhausted or is available in a reduced quantity, the control system can supplement fuel delivery by the second fuel injector with fuel from the first fuel storage tank.
As another example, the control system may be configured to: during a first operating condition, operate the fuel pump to supply fuel from the first fuel storage tank to the first fuel passage at a lower pressure while operating the port fuel injector to deliver to the cylinder the fuel received from the first fuel storage tank; and during a second operating condition, operate the fuel pump to supply fuel from the first fuel storage tank to the first fuel passage at the higher pressure while transferring at least a first portion of the fuel from the first fuel storage tank to the second fuel storage tank via the pressure relief valve. In this way, the fuel delivery system may be operated to selectively transfer fuel from a first fuel storage tank to a second fuel storage tank to maintain at least a threshold or minimum amount of fuel in the second fuel storage tank.